Technical Field
This disclosure relates to an automatic document feeder having two document sheet trays, an image reading device incorporating the automatic document feeder, and an image forming apparatus incorporating the image reading device with the automatic document feeder.
Related Art
General multifunction printers (MFPs) include an image reading device disposed above the printer, and an automatic document feeder (hereinafter, ADF) disposed above the image reading device. Such ADFs includes one or more image reading methods to read an image formed on an original document sheet. For example, a known image reading device employs two image reading methods, which are a sheet through type in which a fixed reading member reads an image formed on an original document sheet set on a document table that is a first document sheet tray while conveying the original document sheet, and a fixed reading type in which an original document sheet is set on a bypass tray that is a second document sheet tray attached to a side face of the ADF and a fixed image reading member reads an image formed on the original document sheet.
When the original document sheet is set on the second document sheet tray and is then contacted to a scan entrance roller, a bypass document set sensor detects presence of the original document sheet and the scan entrance roller rotates. After having been conveyed to a registration sensor, the original document sheet stops. Thereafter, as a user presses a scan start button on a control panel, an image scanning operation starts to read the image while the original document sheet is being conveyed.
Original document sheets conveyed from the second document sheet tray are mainly plastic cards or thick paper sheets. Such plastic cards and thick paper sheets are different from regular original documents and do not bend or are not easily bendable. Therefore, when the original document sheet that is not flexible or elastic is fed from the first document sheet tray, the original document sheet cannot pass a curved portion to be turned and reversed. By contrast, when the original document sheet is fed from the second document sheet tray, the unbendable hard original document sheet including a plastic card and a thick paper sheet that cannot be fed from the first document sheet tray can be conveyed through the entirely straight path.
However, while the fixed reading member is reading an image formed on an original document sheet set to the first document sheet tray is being conveyed, when a different original document sheet set on the second document sheet tray is fed, these original document sheets contact with each other, resulting in a paper jam.
In order to avoid such collision of multiple original document sheets in the image reading device, when an original document sheet is set to the second document sheet tray during regular document conveyance from the first document sheet tray, the bypass document set sensor is turned on, and document conveying rollers is stopped driving. Then, the conveyance of the original document sheet conveyed from the first document sheet tray is controlled to stop as a document paper jam.